In order to extend the life, improve the kinematic performance, reduce the weight and lower the cost of automobile tires, it is known to embed a steel cord, in which multiple wires made of steel are arrayed in parallel with one another, in the belt layer that constitutes the tire.
Patent Document 1 discloses a steel cord in which a steel wrapping wire is wound helically on multiple steel wires arrayed in parallel with one another. Accordingly, if the binding force produced by the steel wrapping wire is too great, a strong contact pressure acts between the multiple steel wires, fretting wear develops at the time of use (when the vehicle is traveling with the tire mounted) and there is the danger of a decline in durability. Patent Document 2 discloses an arrangement in which multiple steel wires are wrapped by an organic fiber rather than by a steel wrapping wire. However, since organic fiber has much less rigidity in comparison with steel, there is the danger that the force that maintains the parallel arrangement of the multiple steel wires will be inadequate. If the number of steel wires to be arrayed in parallel is large, loss of shape is especially likely to occur.
Arrangements in which multiple wires (filaments) are united in parallel with one another using an adhesive rather than a wrapping wire have been proposed (Patent Documents 3 and 4).
Maintaining multiple steel wires in a mutually parallel state using an adhesive rather than by winding a wrapping wire around them eliminates the need to consider the magnitude of binding force and the like that should be taken into consideration when use is made of a wrapping wire. If an adhesive is used, however, the adhesion between steel wires provided by the adhesive must be taken into account as a matter of course. In addition, since the adhesive lies between the steel cord and the rubber, it is necessary to consider the rubber adhesion with respect to the steel cord when the steel cord is embedded within the rubber (the belt layer). It is of course necessary to also consider the relationship between the adhesive strength afforded by the adhesive and the repulsive force of the steel cord (a force that flexure) in order to assure shape stability.    Patent Document 1: Japanese Patent Application Laid-Open No. 62-149929    Patent Document 2: Japanese Patent Application Laid-Open No. 2001-55008    Patent Document 3: Japanese Patent Application Laid-Open No. 63-240402    Patent Document 4: Japanese Patent Application Laid-Open No. 7-304307